Neutrophils have been implicated as the major cellular mediator in many forms of acute lung injury including the acute respiratory distress syndrome (ARDS). Events that control neutrophil-mediated inflammation are poorly understood and even less is known about the ability of acute phase proteins to regulate inflammatory processes resulting in acute lung injury. The objective of the proposed research is to test the fundamental hypothesis that the acute phase reactant, C-reactive protein (CRP), alters neutrophil and endothelial cell functions and thereby modulates neutrophil-mediated insults to endothelium. A specific hypothesis is that CRP alters mitogen-activated protein (MAP) kinase signal transduction with consequences on cytoskeletal structure and related functions. The experimental approach focuses upon an examination of control mechanisms by CRP of neutrophil-mediated injury to cultured endothelial cells and in neutrophils and endothelial cells individually. The specific aims are: 1) to determine whether CRP binds a specific receptor as a mechanism of inhibition of neutrophil movement which thereby alters cell functions of adherence, F-actin content and distribution, cell morphology and MAP kinase activities in isolated human neutrophils; 2)to contractile force, F-actin content and distribution, cell morphology and MAP kinase activities in human umbilical vein endothelial cells; and 3) to determine whether CRP modulates neutrophil-mediated endothelial cell injury (neutrophil adhesion to endothelial cells, neutrophil-mediated permeability of endothelial cells, transendothelial cell migration and neutrophil-mediated cytotoxicity of endothelial cells), potentially through a MAP kinase pathway. Mechanisms of regulation by CRP will be determined by measurement of its effect on selective yet distinct steps involved in neutrophil activation and function. Results of these biochemical and cell biological studies will provide valuable information on the role of CRP in neutrophil and endothelial cell signal transduction and resolution of neutrophil-mediated acute inflammatory injury. The results of this research will also provide valuable support for the potential therapeutic role of CRP in acute, pathological immune reactions, such as ARDS.